Numbers are not yet known for the 2nd stage retrieval or Falcon Heavy. One could probably assume a similar number for the first stage but possibly a bit less given the Falcon Heavy's higher thrust/weight ratio.
An enormous amount of inertia to overcome so 30% doesn't sound so unlikely.
1. Alter the path so the parabolic arc goes back to the launch site.
2. Braking burn during descent to minimize atmospheric stress.
3. Landing burn (AKA "suicide burn") to slow the vehicle enough for the landing legs to absorb the impact.
Though it's not quite that simple. Based on the trajectory of last week's launch, they're actually going to use a much steeper trajectory during the first stage launch. The result is that the first stage uses significantly less propellant to make that first burn (since its downrange velocity is much smaller), but it cuts into the payload capacity quite a bit by forcing the second stage to do more work.
(I didn't know that)
The second stage will need a re-entry heat shield, but otherwise can land like the first. Tricky part is getting enough margin in the second stage for the landing fuel and legs and heat shield. Usually the top stage is the one you optimize most heavily. So plausible, but tricky.
Good news is that the second stage is much cheaper than the first, at least on the F9. Eight fewer engines, for one.
Edit: Found the original copy on the Web Archive http://web.archive.org/web/20110615000000*/http://www.spacex...
Even if I were an expert, the starting point is asking the question, and if I made claims about the answer, someone would come along and say it is still unknown as to whether they can do that.
It should be framed as a question because it is an open question. That's the way technology works. You don't really know you can do something until you do it.
So this question is an attempt to inform you and others of the correct context for discussion. Of course it failed.
However, once the F9 v1.1 has been thoroughly tested in the reusable configuration they will stop offering the expendable option. Every flight will have the first stage flyback for reuse, and only payloads which allow that flight profile will be flown, leaving more than enough fuel margin to allow return and some contingency.
Larger payloads will simply be flown on the Falcon Heavy, which will reuse the lower stage cores from day one. Even if that means no cross-feed and a massive hit to the payload capacity the Falcon Heavy should still be able to loft payloads larger than the Delta IV Heavy and with reusability it should be able to do so at less than the current cost of the F9.
That's expendable launch (at reusable prices!) every 5-10+ launches per vehicle.
Has SpaceX really cracked that problem? What portion of flights on this smaller rocket can do it? It says some missions won't have enough fuel left over.
Will the Falcon 9 Heavy be able to do all or almost all missions with a landing and full recovery at the end? How much fuel will Heavy have left on average after a return? Theoretically it would not wait until the last possible second to start slowing, and therefore use up almost all of the fuel in order to give the descent a larger margin of error and also reduce the possibility of damage, I assume.